70's atari power supply not working

dyno

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I have an atari game from the 70's which is not showing anything on the screen, the monitor works fine but no picture. It seems that the power supply isn't doing much, where should I start to look for problems? This is my first encounter with one of these power supplies that doesn't work, it has the Big Blue Cap on it.
 
The game is Avalanche made in 1978, there is no bridge rectifier on it, it has 5 fuses on it. I will try to take a picture tonight of it and post.
 
It actually is the original KABOOM from what I have read about it. When I came across the add I thought it looked cool and they wanted it gone so I made an offer of $50 which they accepted, when I went to pick it up they said that the monitor wouldn't go on after they moved it so I could have it for $25. Turned out one of the interlock switches that was taped down popped up killing power to the game, so that was why the monitor wouldn't turn on. As promised here are the pictures of the power supply, I don't seem to be getting any +5 v. The one fuse was by passed somewhere along the line for some reason that is why there is a fuse missing.
 

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It looks like you are missing at least one fuse and the small board on the bottom of the power suply needs to be checked out, it creates the +5 according to the manual. The voltage regulator on it might have died after all of these years.
 
There is no voltage regulator on that board, the only thing on there are the diodes. The board connects to the big blue capacitor, is that what regulates the voltage for it?
 
You wont get +5VDC off that power supply as it doesn't output +5VDC.

I'm fairly familiar with this particular power assembly - it was used extensively by Atari for about a dozen of so B&W raster games in the late 70s - also used in 1980 for the Atari Missile Command upright - I know this because I managed to blow the transformer in my Missile Command and its just taken me two months to source a replacement ...

Anyway - enough of that.

There's a 12 pin molex on the right hand side of the power assembly. 4 columns of 3 pins. Column 1 = pins 1-3 from top to bottom, colums 2 = pins 4-6 etc.

Using a multi-meter look for the following readings:

Pins 1&2 = 10.3VDC (unregulated so might read about 12VDC)
Switch the meter to AC:
Pins 4&6 = 25VAC
Pins 4&5 = 12.5VAC
Pins 11&12 = 6.3VAC

Report back, then we'll take it from there.
 
My readings are not even close to those, I am not even getting a full number. Everything seems to be in the .2 etc. I can feel the transfomer "humming", now if it is the transformer I do have a few other atari power supplies which don't look similar but have transformers on them, can I use one of those transformers as a replacement?
 
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Took another look at it again and there doesn't seem to be not much power coming out of the side of the transformer that goes to the 12 pin molex connector and fuses on that side.
 
Hmm ..... not looking good ....

You could take things back a stage further:

The 25VAC comes directly off the transformer, but it does pass through fuses F3&F4 before it hits the molex, so might be worth taking a reading before the current passes through those fuses.

The 10.6VDC comes off the rectifier (or arrangement of four diodes if you prefer) so again, you may want to check what AC voltage the transformer is supplying into the rectifier.

That said, the 6.5VAC comes straight off the transformer and into the molex (there is a fuse for that, but it's usually buried on the floor of the cab, close to the on/off switch so you can rule that out) so it looks like the transformer isn't doing it's job.

Which leads me to conclude that you've got a duff transformer. It's odd, as the transformer is clearly giving you the 125VAC that you need to run the monitor, so I'd say one/two/more of the windings inside the transformer have blown - which is highly unusual.

I say unusual .... but the transformer side of the assembly is protected by fuses F1&F2, and someone has bypassed F2 which might explain it.

Solution ...... I guess you could in theory replace the transformer - but it needs to output the same set of voltages as the one you do have should output, and I doubt it would be an easy job anyway. I reckon you need a replacement power assembly. I can post a partial list of suitable donor cabs later.
 
Possible donor cabs for the required power assembly:

Sprint 4
Video Pinball
Avalanche
Ultra Tank
Subs
Destroyer
Basketball
Canyon Bomber
Monte Carlo
Super Breakout
Missile Command (if you really must ...)
 
I am thinking the same thing, that the transformer is shot. It only has 2 rectifier diodes on it and the monitor actaully has its own transformer, and since the F2 fuse is suppose to is missing and protects that side of the transfomer, like you said it might be gone. I have actaully found a replacement power supply for it already but I just want to make sure before I go and buy the new one. I will check those areas on the pwer supply you mentioned to make sure I haven't missed something.
 
I have an atari game from the 70's which is not showing anything on the screen, the monitor works fine but no picture. It seems that the power supply isn't doing much, where should I start to look for problems? This is my first encounter with one of these power supplies that doesn't work, it has the Big Blue Cap on it.

Get rid of the original power supply, bypass the on-board regulators, and put a switcher in in it's place... you'll be much happier in the long run.

The original atari supplies were unreliable and inefficient, and just generate a lot of excess heat.
 
I am thinking the same thing, that the transformer is shot. It only has 2 rectifier diodes on it and the monitor actaully has its own transformer, and since the F2 fuse is suppose to is missing and protects that side of the transfomer, like you said it might be gone. I have actaully found a replacement power supply for it already but I just want to make sure before I go and buy the new one. I will check those areas on the pwer supply you mentioned to make sure I haven't missed something.
Good news that you've got a replacement. Quick word of caution though - and this is all guess work on my part, but I suspect that something was shorting on the AC wiring harness (possibly interlocks / power on/off) that caused F2 to blow and keep blowing. Rather than track that problem down it's possible that someone decided to bypass the fuse altogether (which resulted in the blown transformer).

So - don't be too suprised if a replacement power assembly blows fuse F2 on pwer up - if it does then check interlocks/power on/off.

Best of luck with it.
 
Well I screwed up, the power supply is fine. I was measuring it wrong, I took another look at it today and I am getting all the correct power measurements out of the 12 pin molex connector. They are all bang on to what they should be, so know I have elimnated the pwer supply as the problem I guess I need to look at the pcb board or rf shield that connects to it. Is it possible that the Big Blue capacitor or bridge rectifier diodes are the problem?
 
Ah well - at least you know its working.

I'd leave that side of the equation alone for now and switch your attention to the PCB. The 10VDC unregulated should show up at pins 2 & B of the PCB. The PCB regulates the 10VDC down to 5VDC which is what the game needs to run.

Test to make sure the 10VDC is going in where it should, then start looking for the 5VDC - try pins J&M = red multi-meter probe to J, black to M. See what ouput you can find. If it's above/below 5VDC there's a small pot on the PCB to adjust up&down (no idea where, but if you can't find it easily then just look at where the traces lead you from those two pins).

Take a look at pages 38 and 78 of the manual if that helps. If you can nail the 5VDC you might be in luck - if not then thats probably where I bow out as if you've got the 5VDC but no game then there's a problem that's likely nothing to do with power/signal dustribution which is about as much as I know.
 
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